The present invention relates to a resin composition and an injection-molded article. Particularly, the present invention relates to a resin composition that can provide a molded article superior in mold release properties, flexibility and heat resistance, especially when used in injection molding, and to the injection-molded article. The improved release properties of the resin composition according to the present invention are very desirable for the finish and productivity of the molded article. The resin composition according to the present invention is most suitably used for making, in particular, injection-molded articles to which are required flexibility and heat resistance, such as containers, caps, packings and gaskets.
As resin compositions for obtaining articles that are required to have flexibility and heat resistance, such as containers, caps, packings and gaskets, by an injection molding method, there are known resin compositions disclosed in JP-A-6-313072 and JP-A-7-316352.
The former reference discloses a resin composition comprising a copolymer of ethylene and an xcex1-olefin of 4 or more carbon atoms which has specific properties and an olefin polymer such as a high-pressure-produced low-density polyethylene or a linear low-density polyethylene. The latter reference discloses a resin composition comprising an ethylene-xcex1-olefin copolymer having a relatively low density and a relatively low highest melting peak temperature measured with a differential scanning calorimeter (hereinafter referred to also as DSC) and an ethylene-xcex1-olefin copolymer having a relatively high density and a relatively high highest melting peak temperature measured with DSC.
The resin compositions disclosed in the above references, however, involve problems such as unsatisfactory mold release properties as an injection-molded article and insufficient flexibility and heat resistance as the resulting molded article.
An object of the present invention is to provide a resin composition that can provide a molded article superior in mold release properties, flexibility and heat resistance, particularly when used in injection molding, and the injection-molded article.
The present inventor has earnestly done investigation in order to achieve the above object. As a result, the present inventor found that a resin composition comprising an ethylene-xcex1-olefin copolymer having specific properties, an ethylene homopolymer or ethylene-xcex1-olefin copolymer having specific properties, and a low-density polyethylene obtained by a high-pressure radical polymerization method and having specific properties can achieve the above object, whereby the present invention has been accomplished.
That is, the present invention relates to a resin composition comprising:
(A) an ethylene-xcex1-olefin copolymer meeting the following conditions (A-1), (A-2) and (A-3):
(A-1) the melt flow rate (MFR) is in the range of from 0.5 to 100 g/10 min,
(A-2) the density is in the range of from 860 to 920 kg/m3, and
(A-3) the highest melting peak temperature determined with a differential scanning calorimeter is in the range of from 50xc2x0 C. to 110xc2x0 C.;
(B) an ethylene homopolymer or ethylene-xcex1-olefin copolymer meeting the following conditions (B-1), (B-2) and (B-3):
(B-1) the melt flow rate (MFR) is in the range of from 0.5 to 100 g/10 min,
(B-2) the density is in the range of from 910 to 980 kg/m3, and
(B-3) the highest melting peak temperature determined with a differential scanning calorimeter is in the range of from 110xc2x0 C. to 135xc2x0 C.; and
(C) a low-density polyethylene as high-pressure radical polymerization product which meets the following conditions (C-1) and (C-2):
(C-1) the melt flow rate (MFR) is in the range of from 0.5 to 100 g/10 min, and
(C-2) the swell ratio (SR) is in the range of from 1.3 to 2.0, said resin composition comprising 40 to 90% by weight of component (A), 5 to 30% by weight of component (B) and 5 to 30% by weight of component (C) when the total proportion of component (A), component (B) and component (C) is taken as 100% by weight.
In addition, the present invention relates to an injection-molded article comprising the above-mentioned composition.
The ethylene-xcex1-olefin copolymer (A) used in the present invention refers to a copolymer of ethylene and one or more xcex1-olefins of 3 to 12 carbon atoms. The xcex1-olefins include, for example, propylene, butene-1, pentene-1, 4-methyl-1-pentene, hexene-1, octene-1 and decene-1. Of these, propylene, butene-1, hexene-1 and octene-1 are preferable, and butene-1 and hexene-1 are more preferable.
The content of the structural units derived from ethylene (hereinafter referred to as xe2x80x9cethylene unitsxe2x80x9d) in component (A) is preferably in the range of from 65 to 95% by weight, more preferably from 68 to 90% by weight. The content of the structural units derived from the xcex1-olefin(s) (hereinafter referred to as xe2x80x9cxcex1-olefin unitsxe2x80x9d) in component (A) is preferably in the range of from 5 to 35% by weight, more preferably from 10 to 32% by weight.
Component (A) includes, for example, ethylene-propylene copolymers, ethylene-butene-1 copolymers, ethylene-4-methyl-1-pentene copolymers, ethylene-hexene-1 copolymers, ethylene-octene-1 copolymers and ethylene-propylene-butene-1 terpolymers. Of these, ethylene-propylene copolymers, ethylene-butene-1 copolymers, ethylene-hexene-1 copolymers and ethylene-octene-1 copolymers are preferable, and ethylene-butene-1 copolymers and ethylene-hexene-1 copolymers are more preferable.
The melt flow rate (hereinafter referred to also as MFR) of component (A) is in the range of from 0.5 to 100 g/10 min, preferably from 1 to 50 g/10 min, more preferably from 2 to 25 g/10 min. When MFR is less than 0.5 g/10 min, the resulting resin composition has an insufficient flowability and hence it has a low injection moldability in some cases. On the other hand, when MFR is more than 100 g/10 min, an injection-molded article having an insufficient strength is obtained in some cases.
The density of component (A) is in the range of from 860 to 920 kg/m3, preferably from 863 to 910 kg/m3, more preferably from 865 to 905 kg/m3. When the density is less than 860 kg/m3, the resulting injection-molded article has an insufficient heat resistance in some cases. On the other hand, when the density is more than 920 kg/m3, the resulting injection-molded article has too high a stiffness and hence an insufficient flexibility in some cases.
The highest melting peak temperature of component (A) determined with a differential scanning calorimeter is in the range of from 50xc2x0 C. to 110xc2x0 C., preferably from 55xc2x0 C. to 100xc2x0 C., more preferably from 60xc2x0 C. to 90xc2x0 C. When said peak temperature is lower than 50xc2x0 C., the resulting injection-molded article has an insufficient heat resistance in some cases. On the other hand, when said peak temperature is higher than 110xc2x0 C., the resulting injection-molded article has too high a stiffness and hence an insufficient flexibility in some cases.
A process for producing component (A) is not limited, and a well-known copolymer may be used as component (A). A preferable production process of component (A) is a process comprising copolymerizing ethylene with one or more xcex1-olefins in the presence of a metallocene-based catalyst. The metallocene-based catalyst includes, for example, catalysts comprising a metallocene complex and an aluminoxane, and catalysts comprising a metallocene complex and an organoaluminum compound and/or a boron compound. Specific examples of the metallocene-based catalysts are a catalyst comprising dimethylsilylene(tetramethylcyclopentadienyl)(3-tert-butyl-2-phenoxy)titanium dichloride, triisobutyl-aluminum and N,N-dimethylanilinium (pentafluorophenyl)-borate (see JP-A-9-87313) and a catalyst comprising dimethylsilylene(tetramethylcyclopentadienyl)(3-tert-butyl-2-phenoxy)titanium dimethoxide, triisobutyl-aluminum and N,N-dimethylanilinium (pentafluorophenyl)-borate (see JP-A-10-259211).
As to the ethylene homopolymer or ethylene-xcex1-olefin copolymer (B) used in the present invention, the ethylene homopolymer refers to a polymer consisting of ethylene units alone, and the ethylene-xcex1-olefin copolymer refers to a copolymer of ethylene and one or more xcex1-olefins of 3 to 12 carbon atoms. The xcex1-olefins include, for example, propylene, butene-1, pentene-1, 4-methyl-1-pentene, hexene-1, octene-1 and decene-1. Of these, propylene, butene-1, hexene-1 and octene-1 are preferable, and butene-1 and hexene-1 are more preferable.
In the ethylene-xcex1-olefin copolymer as component (B), the content of ethylene units is preferably in the range of from 90 to 100% by weight, more preferably from 93 to 99% by weight, and the contents of xcex1-olefin units is preferably in the range of from 0 to 10% by weight, more preferably from 1 to 7% by weight.
The ethylene-xcex1-olefin copolymer as component (B) includes, for example, ethylene-propylene copolymers, ethylene-butene-1 copolymers, ethylene-4-methyl-1-pentene copolymers, ethylene-hexene-1 copolymers, ethylene-octene-1 copolymers and ethylene-propylene-butene-1 terpolymers. Of these, ethylene-propylene copolymers, ethylene-butene-1 copolymers, ethylene-hexene-1 copolymers and ethylene-octene-1 copolymers are preferable, and ethylene-butene-1 copolymers and ethylene-hexene-1 copolymers are more preferable. Ethylene homopolymers are also more preferable as component (B).
The melt flow rate (MFR) of component (B) is in the range of from 0.5 to 100 g/10 min, preferably from 1 to 70 g/10 min, more preferably from 5 to 60 g/10 min. When the MFR is less than 0.5 g/10 min, the resulting resin composition has an insufficient flowability and hence it has a low injection moldability in some cases. On the other hand, when the MFR is more than 100 g/10 min, an injection-molded article having an insufficient strength is obtained in some cases.
The density of component (B) is in the range of from 910 to 980 kg/m3, preferably from 915 to 965 kg/m3, more preferably from 920 to 950 kg/m3. When the density is less than 910 kg/m3, the resulting injection-molded article has an insufficient heat resistance in some cases. On the other hand, when the density is more than 980 kg/m3, the resulting injection-molded article has too high a stiffness and hence an insufficient flexibility in some cases.
The highest melting peak temperature of component (B) determined with a differential scanning calorimeter is in the range of from 110xc2x0 C. to 135xc2x0 C., preferably from 115xc2x0 C. to 135xc2x0 C., more preferably from 120xc2x0 C. to 132xc2x0 C. When said peak temperature is lower than 110xc2x0 C., the resulting injection-molded article has an insufficient heat resistance in some cases. On the other hand, when said peak temperature is higher than 135xc2x0 C., the resulting injection-molded article has too high a stiffness and hence an insufficient flexibility in some cases.
A process for producing component (B) is not limited, and a well-known homopolymer or copolymer may be used as component (B). A preferable production process of component (B) is a process comprising polymerizing ethylene alone or copolymerizing ethylene with one or more xcex1-olefins, by the use of a Ziegler-Natta catalyst in the presence or absence of a solvent usually at 30xc2x0 C. to 300xc2x0 C. and at atmospheric pressure to 300 MPa. The Ziegler-Natta catalyst is not limited. Preferable examples of the Ziegler-Natta catalyst are catalysts comprising a solid catalyst component containing a titanium atom, a halogen atom and an Mg atom and an organoaluminum compound. More preferable examples of the Ziegler-Natta catalyst are catalysts comprising a solid catalyst component containing a titanium atom, a halogen atom and an Mg atom, an organoaluminum compound and a silicon compound. Specific examples of the Ziegler-Natta catalyst are catalysts comprising (TiCl3.(⅓)AlCl3) (MgCl2)n, a trialkylaluminum and a silicon compound (see JP-A-1-69609).
The low-density polyethylene as high-pressure radical polymerization product (C) used in the present invention is a low-density polyethylene obtained by a high-pressure radical polymerization method. Here, the high-pressure radical polymerization method is a well-known polymerization method, is not particularly limited and means a method in which a polymer is produced by allowing polymerization to initiate and proceed under a high pressure by the use of a radical-generating agent. As a generally practiced high-pressure radical polymerization method, a method can be In exemplified in which a polymer is produced by allowing polymerization to initiate and proceed by the use of a radical-generating agent (e.g., a peroxide and oxygen) in a vessel reactor or a tubular reactor under conditions of a polymerization pressure of 100 to 300 MPa and a polymerization temperature of 130xc2x0 C. to 300xc2x0 C. The melt flow rate of the resulting polymer can be controlled by using a hydrocarbon (e.g., methane and ethane) or hydrogen as a molecular weight regulator. The swell ratio (hereinafter referred to also as SR) and density of the polymer can be controlled by properly choosing the polymerization temperature and pressure within the above ranges.
The melt flow rate (MFR) of component (C) is in the range of from 0.5 to 100 g/10 min, preferably from 1 to 50 g/10 min, more preferably from 2 to 25 g/10 min. When the MFR is less than 0.5 g/10 min, the resulting resin composition has an insufficient flowability and hence it has a low injection moldability in some cases. On the other hand, when the MFR is more than 100 g/10 min, an injection-molded article having unsatisfactory mold release properties is obtained in some cases.
The swell ratio (SR) of component (C) is in the range of from 1.3 to 2.0, preferably from 1.55 to 1.95, more preferably from 1.60 to 1.90. When the SR is less than 1.3, an injection-molded article having unsatisfactory mold release properties is obtained in some cases. On the other hand, when the SR is more than 2.0, an injection-molded article having an insufficient surface gloss is obtained in some cases.
The density of component (C) may be any density so long as it is low. It is preferably in the range of from 910 to 930 kg/m3, more preferably from 915 to 925 kg/m3.
The proportions of components (A) through (C) are as follows: the proportion of component (A) is in the range of from 40 to 90% by weight, preferably from 55 to 84% by weight, more preferably from 59 to 84% by weight; the proportion of component (B) is in the range of from 5 to 30% by weight, preferably from 8 to 25% by weight, more preferably from 8 to 23% by weight; and the proportion of component (C) is in the range of from 5 to 30% by weight, preferably from 8 to 20% by weight, more preferably from 8 to 18% by weight. Here, the total proportion of component (A), component (B) and component (C) is taken as 100% by weight.
When the proportion of component (A) is less than 40% by weight, the resulting injection-molded article has too high a stiffness and hence an insufficient flexibility in some cases. On the other hand, when the proportion is more than 90% by weight, the resulting injection-molded article has an insufficient heat resistance in some cases.
When the proportion of component (B) is less than 5% by weight, the resulting injection-molded article has an insufficient heat resistance in some cases. When the proportion is more than 30% by weight, the resulting injection-molded article has too high a stiffness and hence an insufficient flexibility in some cases.
When the proportion of component (C) is less than 5% by weight, the resulting injection-molded article has unsatisfactory mold release properties in some cases. On the other hand, when the proportion is more than 30% by weight, the resulting injection-molded article has too high a stiffness and hence it has an insufficient flexibility in some cases.
The mold shrinkage factor of the injection-molded article of the present invention is not limited and is preferably in the range of from 1.2 to 1.6%, more preferably from 1.2 to 1.4%. When the mold shrinkage factor is less than 1.2%, the resulting injection-molded article has unsatisfactory mold release properties in some cases. On the other hand, when the mold shrinkage factor is more than 1.6%, the resulting injection-molded article is distorted or has no stable dimensions in some cases.
A process for producing the resin composition of the present invention is not limited and may be a well-known process. As said production process, a process can be exemplified in which component (A) through (C) are uniformly mixed by a method such as a tumbler blender method, Henschel mixer method, Banbury mixer method or piston granulation method.
If necessary, components (A) through (C) used in the present invention may be used in combination with conventional additives such as stabilizers (e.g., antioxidants), neutralizing agents, dispersing agents, lubricants, weather resistance improvers, antistatic agents, pigments and fillers so long as the additives do not affect the object of the present invention.
The antioxidants include, for example, phenolic stabilizers such as n-octadecyl-3-(4xe2x80x2-hydroxy-3,5xe2x80x2-di-t-butylphenyl) propionate (IRGANOX 1076, a trade name) and phosphite stabilizers such as bis(2,4-di-t-butylphenyl)-pentaerythritol diphosphite and tris(2,4-di-t-butylphenyl) phosphite. The neutralizing agents include, for example, hydrotalcite and calcium stearate. The lubricants include, for example, higher fatty acid amides and higher fatty acid esters. The antistatic agents include, for example, glycerol esters of fatty acids of 8 to 22 carbon atoms, sorbitan acid esters and polyethylene glycol esters.
If necessary, components (A) through (C) used in the present invention may be used in combination with at least one of various resins so long as the resins do not affect the object of the present invention. As resins for controlling physical properties such as stiffness of the resulting resin composition, there can be exemplified resins such as polypropylenes, ethylene-vinyl acetate copolymers, ethylene-methyl methacrylate copolymers, ethylene-ethyl acrylate copolymers, etc.